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    <head>
        <meta charset="utf-8">
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        <title>clear float</title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <style>
            .father::after {
                content: ".sdds";
                height: 0;
                display: block;
                visibility: hidden;
                clear: both;
            }

            .son1 {
                float: left;
            }
            .son1,
            .son2   { 
                width: 100px;
                height: 100px;
                border: 1px solid rgb(52, 201, 84);
            }
        </style>
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        <div class="father">
            <div class="son1">1</div>
            <div class="son2">2</div>
        </div>
    </body>
</html>